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Stockholders' Equity - Additional Information (Detail) - USD ($)
 12 Months Ended
Oct. 24, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Class of Stock [Line Items]        
Preferred stock, shares authorized   10,000,000 10,000,000  
Preferred stock, par value   $ 0.0001 $ 0.0001  
Preferred stock, shares designated   0 0  
Preferred stock, shares issued   0 0  
Preferred stock, shares outstanding   0 0  
Proceeds from sale of common stock $ 189,700,000      
Common stock, shares authorized   300,000,000 300,000,000  
Maximum 401(k) per employee, percentage of annual salary   60.00%    
Matching 401(k) employer contribution, maximum amount   $ 4,000    
Compensation expense in connection with 401(k) retirement plan   $ 1,600,000 $ 1,100,000 $ 900,000
Change in control severance payment period for executives   12 months    
Change in control severance payment period for employees   6 months    
Change in control cash severance payment for chief executive officer   24 months base salary plus annual target incentive pay    
Employee Stock Purchase Plan [Member]        
Class of Stock [Line Items]        
Common stock, shares authorized   2,500,000    
Percentage of purchase price of stock   85.00%    
2017 Performance Incentive Plan [Member]        
Class of Stock [Line Items]        
Number of common stock shares available for stock options grants   8,300,000    
Share-based compensation plan's share limit reduction for every one restricted stock unit granted   1.5    
Stock options term under equity incentive plans   8 years    
2017 Performance Incentive Plan [Member] | Director [Member]        
Class of Stock [Line Items]        
Service period for stock-based compensation award granted   1 year    
2017 Performance Incentive Plan [Member] | Stock Options [Member] | Employee [Member]        
Class of Stock [Line Items]        
Service period for stock-based compensation award granted   4 years    
2017 Performance Incentive Plan [Member] | Stock Options [Member] | Director [Member]        
Class of Stock [Line Items]        
Service period for stock-based compensation award granted   1 year    
2017 Performance Incentive Plan [Member] | Restricted Stock Units (RSU) [Member] | Employee [Member]        
Class of Stock [Line Items]        
Service period for stock-based compensation award granted   3 years    
Common Shares [Member]        
Class of Stock [Line Items]        
Sale of common stock, Shares 14,950,000   14,950,000  
Underwriting commissions and discounts $ 12,100,000      
Legal, accounting fees, filing fees and other offering expenses $ 400,000      
Common stock, shares reserved for issuance in equity compensation plans   26,761,122